Water Flow and Aeration in the Aquarium.
An aquarium contains various living organisms: fish, plants, and nitrifying bacteria. They constantly consume oxygen and will begin to suffocate and die if aeration is poor (due to lack of oxygen). In addition, a “struggle” for oxygen may well arise between plants and fish; despite the fact that plants also release oxygen, they consume it at night. Nevertheless, keeping plants in the aquarium is extremely important because the carbon dioxide exhaled by fish is absorbed by plants during daylight hours—in other words, they serve as a kind of balancing tool.
Apart from its direct necessity for plants and animals, oxygen is needed by special bacteria known as nitrifying bacteria. In an aquarium where there is an oxygen deficiency, they cannot develop normally, and consequently, the effect of their activity will be zero or close to it. Furthermore, waste products from the fish will constantly appear in the aquarium, which in turn release toxins; oxygen helps accelerate the process of breaking down toxins and other gases, which is again extremely beneficial for water quality.
If we want to recreate conditions natural to the biotopes of our ornamental fish in the aquarium, we must proceed from the fact that most fish inhabit flowing water — fast or moderate. Even if the bulk of the current has a high flow velocity, fish still live in areas where resisting fast water does not require great effort from them. Aeration should be carried out using a filtration system designed to provide maximum water circulation and, if possible, surface agitation. Aeration can also be accomplished using an air pump (a micro-compressor and air stone).
One of the primary purposes of aeration is mixing the water layers in the aquarium. The thermal heater warming the water is usually located in a corner. The compressor should be placed near the heater so that different temperature zones are not created in the aquarium. Streams of warm water quickly rise to the surface, and most of the warm water remains near the heater. The movement of bubbles evenly mixes the water, thereby preventing the lower layers of the aquarium water from remaining unheated. Aquarium water is enriched with oxygen through the surface by contacting the air. As a result, there is more oxygen in the upper layers than in the lower ones. Aeration helps mix the upper and lower water layers faster.
Air from the compressor is forced through a hose into a distributor located near the bottom — the bubbles pull the bottom layer of water toward the surface, helping it become saturated with oxygen. This creates a stream of air bubbles that also promotes water circulation and the formation of ripples on the surface. Oxygen bubbles, upon reaching the water surface, break up the film that forms. Contrary to widespread belief, air bubbles by themselves add relatively little oxygen to the water. The real benefit comes from their effect on water circulation and surface gas exchange. In most of our aquariums, the current generated by the filter provides the necessary water movement. Whether an electric pump or an airlift handles water transportation is of secondary importance.
Practically speaking, there are two methods of directing filtration water into the aquarium: it is sprayed above the water surface over as large an area as possible (whereby the water can absorb a fairly large amount of oxygen), or an electric pump forces the water coming from the filter inside the tank itself, beneath the surface. In the second case, the water cannot receive air from the surface, and then this crucial process — oxygen intake — must be carried out in another way.
A diffuser is a small device, most commonly made of plexiglass or another plastic, which is usually installed near the filter outlet. A nipple connection on its outer side allows an air hose to be connected to it. Due to the flow of filtration water under pressure, external air enters through the air hose and is forced into the aquarium water along with the filtration water. The diffuser creates a swirl, and the air bubbles pop gently. They are very small and light, and therefore do not rise to the surface too quickly. In addition, using a clamp that regulates the flow rate, one can reduce, increase, and, if necessary, dose the air supply.
Water aeration in the aquarium is one of the vital conditions for the normal existence of living organisms, especially when they are present in significant numbers. Aeration performs the following tasks: • Saturates the water with oxygen; • Creates water circulation in the aquarium; • Evens out the temperature throughout the entire aquarium; • Destroys the bacterial and dust film that forms on the water surface; • Simulates necessary natural conditions, such as a current. These conditions are essential for certain fish species. Aeration promotes a favorable gas exchange regime in the aquarium and enriches the water with the required amount of oxygen. During aeration, vortex currents form on the water surface, facilitating oxygen absorption and carbon dioxide removal.
Fish breathe oxygen and release carbon dioxide, which is consumed by plants during photosynthesis, while plants in turn release oxygen. If the ratio of fish to plants in the aquarium is correctly chosen, these gases are sufficient for them, and they grow and develop wonderfully. In addition, aeration is needed in breeding aquariums, where a large number of fish are kept in a relatively small volume. The smaller the bubbles, the larger their total surface area and the better the oxygen enrichment of the water.
Gas exchange — meaning the enrichment of water with oxygen and the removal of carbon dioxide — occurs mainly at the surface, where air bubbles carry the lower, oxygen-depleted layers of water with them. It also occurs through the walls of the bubbles themselves, which is why they are made as small as possible: increasing the total surface area improves gas exchange conditions. It is especially important to carry out aeration at night, since photosynthesis occurs only in the light during the day, and at night a situation may arise where there is an excess of carbon dioxide and a lack of oxygen in the water. Periodic, short-term, so-called air boosting in the aquarium does little good — it can even harm fish and plants by causing sharp fluctuations in oxygen levels and disrupting their vital activity.
However, while organic content can be very high in densely populated aquariums, this factor can be neglected within reasonable limits in decorative aquariums. Nevertheless, significant deposits of organic matter still occur in such aquariums, both in the substrate and in pre-filters (mechanical filtration compartments). These deposits are especially visible on the sponges of internal filters and similar systems. Most aquarists use canister filters, but they can generally be viewed purely as mechanical filters. The reason is that they cannot actively supply themselves with oxygen on their own.
Biological filtration in an aerobic environment is closely tied to oxygen, which enters closed filters only with the aquarium water. In aquariums using such filters, intensive water aeration is vital. The organic matter generated inside the filter cavities requires significant oxygen consumption; therefore, enriching the water with oxygen is necessary not only to supply the animals but also to replenish the oxygen spent on oxidizing organic matter. Closed-type filters have a drawback: if there is not enough oxygen for nitrification and the organic content exceeds permissible limits, the process proceeds unsatisfactorily, and the filter can “crash” into an anaerobic state.
Signs of excess ammonia and its compounds, protein overload, and decay products can be identified by the formation of persistent foam from the air stone. Air bubbles that rise to the surface should pop within 1–3 seconds. If this does not happen, it means they are in excess in the aquarium. Often, the main source of ammonia is a filter that has not been cleaned for a long time. You should know that the concentration of nitrogenous toxins can reach a critical point very quickly — within 1–2 days. To reduce ammonia toxicity, four rules must be followed: constant aeration, cleanliness in the aquarium, regular water changes, and a moderate population of plants and animals. To limit nitrate levels, regular water changes and mandatory planting are necessary, and excess plants should be removed.
Weekend and vacation feeding blocks should be placed in the zone of water movement from the filter’s water pump or near the air compressor stone. Then the separated particles will be distributed throughout the aquarium; otherwise, they will only be consumed by bottom-dwelling fish. Alternatively, they can be placed 5–7 cm from the water surface (preferably in a fish net), which will provide food for fish at all levels and also save you from pests like snails (especially *Melanoides*), which cover the block so densely that fish simply have nowhere to get to it. White blocks are made of gypsum; such blocks raise the pH as the gypsum dissolves and are not suitable for fish that require acidic water.
Crucial properties and water quality indicators in the aquarium.
What factors influence water oxygenation? 
